If the manned program would quit trying to get ahead of itself, and settle into LONG range plans for manned sustainable presence off world then reasonable tasks would emerge. Initially minimal funding should be used for the manned program in order to determine

1) gravity and radiation effects, and methods to mitigate those effects
2) development of a bootstrapping program that for a consistent and limited budget leads to off world colonization, whether on extraterrestial bodies or space habitats.
3) meaningful support in terms of technology transfer, health information, standards for private utilization of space for media/tourism and eventually mining and colonization.

To accomplish (1) we need to have a gravity simulator which would be best done in orbit or at one of the Lagrangian points. Animal studies could be done relatively cheaply followed by manned studies. Then we would find out if Mars gravity or Moon gravity is livable and under what conditions (sleep in a centrifuge?).

For (2) we should utilize automated and teleoperated probes to first survey, and then start to built infrastructure in order to exploit off world material resources. Once enough infrastructure is built up (access to cheap power, access to water and other basic materials, high bandwidth and pervasive communication capability, robust robotic capabilities), then manned presence can start to be considered.

For (3) NASA could offer some modest "prizes", be generous with licensing developed technology for stuff like radiation shielding and life support equipment, share material survey information and health effects information and avoid undercutting and stepping on fragile private space efforts by offloading work when possible to small space firms.

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This is a long road, because we start the bootstrapping process from so little. There is no way to know exactly what path it will take because you want to follow the optimal cost path. That is dependent on what resources are found and where, and what clever engineering development breakthroughs might be done to make use of them. Several lines of independent goals and tasks could be undertaken for modest budgets. I've list a few examples below.

Currently, reasonable water supplies have only been found on Mars and that is fine on the planet itself but would be too expensive to ship elsewhere. Obviously, we need to find out and have sent multiple probes to test the theoretical possibility of accessible water on the moon. That finding will either create or limit short term opportunities for manned near space access. This is a very critical path operation and should be done as quickly and cheaply as possible (i.e. unmanned probes and robots).

In situ production of cheap solar cells from moon regolith could provide a long term and sustainably cheap power source on the moon. This could provide the energy required to mine and send lunar materials off world.

A very modest budget could be used to explore extremely cheap (alternative) methods of getting material off the moon. There has been some speculative work done in this area already in terms of mass driver designs, and lunar sky hook. It is worth a small budget to determine practicality and requirements of such engineering feats. Obviously, this is one of those bootstrapping game changers if it could done on a reasonable budget.
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Bottom line is that most current manned space activities do not fit into any of the above. The only real possibility might be to add to the ISS in order to do gravity experiments. Otherwise the funding could be better realligned to do the initial (automated and teleoperated) surveys and attempts at engineering breakthroughs.

It is folly to make too many plans(especially expensive manned voyages) until we find out some answers to some of the fundamental problems like the gravity/water issues.